JP7422559B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An image forming apparatus capable of double-sided printing forms an image on the front surface of a sheet, reverses the front and back of the sheet using a reversing mechanism, and forms an image on the back surface of the sheet. Patent Document 1 proposes a reversing mechanism that rotates a sheet along a rotation axis parallel to the conveyance direction of the sheet in order to reverse the front and back of the sheet inside an image forming apparatus.

Patent No. 5779960

Unlike the reversing mechanism that rotates the seat as disclosed in Patent Document 1, there is a known reversing mechanism that reverses the front and back of the sheet by switching back the seat. In order to realize switchback, a gear mechanism and a solenoid are required to switch the direction of rotation of the conveyance roller between normal rotation and reverse rotation. In order to reduce the size of an image forming apparatus, sheet switchback is sometimes achieved by pulling the trailing edge of the sheet from the main conveyance path into the sub-conveyance path while causing the leading edge of the sheet to protrude from the discharge port. Here, when the conveyance speed of the sheet is high, the changeover of the conveyance roller from normal rotation to reverse rotation may not be in time, and the sheet may be discharged from the discharge port, resulting in failure of the switchback. This problem can arise especially with reversing mechanisms that use gears or solenoids, which require switching time. In order to prevent such a reversal error, it is conceivable to lengthen the distance of the conveyance path in which the switchback is performed. However, in this case, the size of the image forming apparatus becomes large. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to reduce the size of an image forming apparatus while also successfully reversing a sheet.

The present invention includes, for example,
A main conveyance path for conveying sheets;
an image forming means for forming an image on a first surface and a second surface of the sheet conveyed through the main conveyance path;
a switchback means provided at the end of the main conveyance path and for switching back the sheet with an image formed on the first surface using a roller;
a sub conveyance path for conveying the switched back sheet to the main conveyance path in order to form an image on the second side of the sheet;
a motor that drives the roller provided in the switchback means and is controlled to rotate only in a certain direction;
a transmission means for transmitting the driving force supplied from the motor to the roller;
switching means acting on the transmission means to switch the direction of rotation of the roller caused by the driving force between normal rotation and reverse rotation;
A first period in which a sheet on which an image is formed on a first surface by the image forming means is conveyed in a first direction by the roller, and a second period in which the sheet is conveyed in a second direction different from the first direction by the roller. At least during the first period of the second period, from a first conveyance speed that is the conveyance speed at which the sheet is conveyed through the image forming means, to a second conveyance speed that is lower than the first conveyance speed. An image forming apparatus is provided, comprising: a control means for controlling the rotational speed of the motor so that the image forming apparatus is conveyed at a speed of 1.

According to the present invention, it is possible to reduce the size of an image forming apparatus and to successfully invert a sheet.

FIG. 1 is a schematic configuration diagram of an image forming apparatus. FIG. 2 is a block diagram showing a controller. FIG. 3 is a diagram illustrating a front-back reversing mechanism. Flowchart illustrating an image forming method. A timing chart showing control timing. 7 is a flowchart showing the image forming method of Example 2. 5 is a timing chart showing control timing of Example 2. FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claimed invention. Although a plurality of features are described in the embodiments, not all of these features are essential to the invention, and the plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and redundant description will be omitted.

<Example 1>
[Image forming device]
As shown in FIG. 1, the image forming apparatus 100 is an electrophotographic printer. Although an electrophotographic method is exemplified as an image forming method here, the present invention is applicable regardless of the image forming method. For example, the present invention is applicable to various methods such as an inkjet recording method and a thermal transfer method.

The replaceable cartridge 120 includes a photosensitive drum 122, a charging roller 123, and a developing roller 121. The photosensitive drum 122 rotates clockwise at a predetermined circumferential speed (process speed). The charging roller 123 uniformly charges the circumferential surface of the photosensitive drum 122. The exposure device 108 irradiates the photosensitive drum 122 with light according to the image signal to form an electrostatic latent image. The developing roller 121 develops the electrostatic latent image using toner to form a toner image.

The feeding roller 102 feeds the sheets stored in the sheet cassette 140 one by one onto the conveyance path. Conveyance roller 103 and registration roller 104 are conveyance rollers that convey the sheet to the transfer section. The transfer section includes a photosensitive drum 122 and a transfer roller 106. When the sheet passes through the transfer section, the toner image is transferred from the photosensitive drum 122 to the sheet. The fixing device 130 applies heat and pressure to the sheet and the toner image to fix the toner image on the sheet. The discharge roller 110 conveys the sheet that has passed through the fixing device 130 to the FD roller 111. FD is an abbreviation for face down. FD is a name derived from the fact that the sheet on which a toner image is formed is discharged with the first surface facing downward.

The FD roller 111 discharges the sheet on which image formation has been completed to the FD tray 112. In double-sided image formation, the FD roller 111 reverses the front and back sides of the sheet on which the image is formed on the first side using a switchback method. Specifically, the FD roller 111 discharges the sheet conveyed through the main conveyance path P1 from the leading edge to the middle of the sheet to the outside of the image forming apparatus 100. At this time, the FD roller 111 is rotating normally. When the rear end of the sheet reaches a position where it can be fed into the sub-transport path P2, the rotation direction of the FD roller 111 is switched from normal rotation to reverse rotation, and the sheet is fed into the sub-transport path. Since the sheet is switched back by the FD roller 111, such a reversing method is called a switchback method. In this way, the FD roller 111 is a conveyance roller that functions as a discharge roller and also as a reversing roller.

The sub conveyance path P2 is a conveyance section extending from the FD roller 111 to the registration roller 104. A plurality of transport rollers 114 are arranged on the sub-transport path P2. These transport rollers 114 transport the sheet toward the registration rollers 104. The registration roller 104 conveys the sheet to the transfer section again. The transfer section transfers the toner image onto the second side of the sheet. The fixing device 130 fixes the toner image on the second side of the sheet. The discharge roller 110 passes the sheet to the FD roller 111. The FD roller 111 discharges the sheet with images formed on both sides to the FD tray 112 by continuing to rotate normally.

A plurality of sheet sensors (eg, registration sensor 105, fixing discharge sensor 109) are provided in the main conveyance path P1. One or more sheet sensors (reversal sensor 113) are provided in the sub-transport path P2. These sheet sensors are generally used to determine whether sheet conveyance is normal, to determine image formation timing, and the like.

[controller]
FIG. 2A shows a controller 200 that controls the image forming apparatus 100. The CPU 201 controls each part of the image forming apparatus 100 by executing a control program stored in the ROM area of the storage device 210. The input circuit 202 receives detection signals output from the registration sensor 105 , fixing/ejection sensor 109 , and reversal sensor 113 and passes them to the CPU 201 . The drive circuit 203 generates a drive current for driving the motor 204 and a drive current for driving the solenoid 205. In this embodiment, motor 204 is a motor that rotates in only one direction. Further, the motor 204 drives and rotates the feeding roller 102, the conveying roller 103, the registration roller 104, the photosensitive drum 122, the transfer roller 106, the fixing device 130, the ejection roller 110, and the FD roller 111. Of these, the FD roller 111 performs normal rotation and reverse rotation in order to switch back the sheet. The solenoid 205 drives a gear mechanism that transmits the driving force supplied from the motor 204 to the FD roller 111, and switches the rotation direction of the FD roller 111. The display device 215, for example, notifies the user of a sheet jam.

FIG. 2B shows functions realized by the CPU 201 executing a control program. Some or all of the multiple functions may be implemented by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

The image formation control unit 220 controls image formation performed by the image forming apparatus 100. The image forming control unit 220 controls charging voltage, developing voltage, and fixing voltage, controls the emission intensity of the exposure device 3, controls the rotation speed of the rotating polygon mirror in the exposure device 3, and controls the fixing temperature of the fixing device 130. I am in charge of such things. For example, the image formation control unit 220 controls the exposure start timing of the exposure device 3 based on the detection result of the registration sensor 105.

The conveyance control unit 230 controls sheet conveyance processing. The speed condition determination unit 231 determines whether a condition for changing the sheet conveyance speed (speed change condition) is satisfied. When the speed change condition is satisfied, the speed condition determination unit 231 instructs the speed change unit 232 to change the conveyance speed (rotational speed of the motor 204). The speed change unit 232 controls the rotational speed of the motor 204 according to a speed change instruction. Specific examples of speed change conditions will be described later.

The direction condition determination unit 233 determines whether a condition (direction change condition) for changing the sheet conveyance direction (rotation direction of the FD roller 111) is satisfied. When the direction change condition is satisfied, the direction condition determination unit 233 instructs the direction change unit 234 to change the conveyance direction. The direction change unit 234 controls the solenoid 205 according to instructions. A specific example of the direction change condition will be described later. The jam detection unit 235 detects a sheet jam based on the detection result of the fixing discharge sensor 109 or the reversal sensor 113.

[Front and back reversal mechanism]
FIG. 3 shows an example of a reversing mechanism 300 using a solenoid 205. FD roller 111 is connected to idler gear 311. In this example, a gear is provided at the end of the rotating shaft of the FD roller 111, and an idler gear 311 meshes with this gear. The idler gear 311 may be composed of a plurality of gears. In this way, the FD roller 111 is rotated by receiving the driving force from the idler gear 311.

The idler gear 311 is connected to a planetary gear 312 and a planetary gear 313. A driving force supplied from the motor 204 is connected to the planetary gear 312 via an input gear 315. When the CPU 201 turns off the solenoid 205 via the drive circuit 203, the switching lever 314 engages with the planetary gear 312. Therefore, the FD roller 111 rotates in the normal rotation direction (the direction in which the sheet is ejected to the outside of the image forming apparatus 100). On the other hand, when the CPU 201 turns on the solenoid 205 via the drive circuit 203, the switching lever 314 meshes with the planetary gear 313. Therefore, the FD roller 111 rotates in the reverse direction (the direction in which the sheet is returned to the inside of the image forming apparatus 100). In a mechanism that switches between normal rotation and reverse rotation using the switching lever 314, there are variations in the response of the solenoid 205 and variations in the operation of the switching lever 314. The time from when the solenoid 205 is turned on until the switching lever 314 completes the switching operation varies by several tens of milliseconds. In conjunction with this, the position of the trailing edge of the sheet (reversal position) when the conveying direction of the sheet is reversed also varies. Due to market demands for image forming apparatuses 100, sheet conveyance speeds are increasing. As the conveyance speed increases, the variation in the reversal position also increases. When the reversal position is on the downstream side of the FD roller 111 in the sheet conveyance direction, the FD roller 111 is no longer able to reverse the sheet. The sheet is ejected to the FD tray 112 even though no image is formed on the second side. Therefore, the CPU 201 needs to drive the solenoid 205 at appropriate timing.

[flowchart]
FIG. 4 shows a method of controlling the image forming apparatus 100 executed by the CPU 201 according to a control program. Here, it is assumed that a double-sided printing job has been submitted.

In S401, the CPU 201 (transport control unit 230) starts the motor 204 and rotates the motor 204 at the first rotation speed. The first rotational speed is a rotational speed corresponding to a so-called image forming speed (process speed). Thereby, the peripheral speeds of the various rollers driven by the motor 204 are maintained at the first conveyance speed (process speed).

In S402, the CPU 201 (image formation control unit 220) controls the image forming apparatus 100 so that an image is formed on the first side of the sheet. The CPU 201 charges the photosensitive drum 122 with the charging roller 123 and supplies an image signal to the exposure device 108 to form an electrostatic latent image. Further, the CPU 201 controls the developing roller 121 to develop the electrostatic latent image to form a toner image. Further, the CPU 201 controls the feeding roller 102 to feed the sheet. For example, the CPU 201 lowers the feeding roller 102 using a solenoid (not shown) to bring the feeding roller 102 into contact with the sheet. As a result, the sheet is sent out to the conveyance path. The CPU 201 controls the exposure start timing of the exposure device 108 based on the timing when the registration sensor 105 detects the leading edge of the sheet. As a result, the toner image is transferred to an appropriate position on the sheet. The CPU 201 controls the fixing device 130 to fix the toner image on the first surface.

In step S<b>403 , the CPU 201 (speed condition determination unit 231 ) determines whether the trailing edge of the sheet has passed a predetermined position based on the detection result of the fixing discharge sensor 109 . For example, when the detection result is switched from ON to OFF, the CPU 201 determines that the trailing edge of the sheet has passed the detection position of the fixing discharge sensor 109. Here, ON means that the sheet is passing, and OFF means that the sheet is not passing. The fixing discharge sensor 109 is arranged downstream of the fixing device 130 in the sheet conveyance direction. That is, the fixing discharge sensor 109 is arranged between the discharge roller 110 and the fixing device 130. The fixing discharge sensor 109 is a sheet sensor for confirming that the trailing edge of the sheet has passed through the fixing device 130. Therefore, the fixing discharge sensor 109 only needs to be disposed between the fixing device 130 and the FD roller 111 in the main transport path P1. When the rear end of the sheet passes the predetermined position, the CPU 201 advances to S404.

In S404, the CPU 201 (speed changing unit 232) reduces the rotational speed of the motor 204 from the first rotational speed to the second rotational speed. The second rotation speed is, for example, 50% of the first rotation speed. The sheet is transported at a second transport speed (50% of the first transport speed) corresponding to the second rotation speed.

In S405, the CPU 201 (direction condition determination unit 233) starts the timer 211. S404 and S405 may be interchanged. The timer 211 may be realized by a count-up type counter circuit or a count-down type counter circuit.

In S406, the CPU 201 (direction condition determination unit 233) determines whether a predetermined time Tb has elapsed from the timing at which the rotational speed was changed, based on the measurement result of the timer 211. When the elapsed time measured by the timer 211 exceeds the predetermined time Tb, the CPU 201 proceeds to S407. Here, the predetermined time Tb is the time required for the rear end of the sheet to arrive at the reversal position where the rear end of the sheet can be pulled from the main transport path P1 to the sub transport path P2.

In S407, the CPU 201 (direction changing unit 234) turns on the solenoid 205 via the drive circuit 203. As a result, the reversing mechanism 300 is activated, and the direction of rotation of the FD roller 111 is changed from normal rotation to reverse rotation. Thereby, the sheet is guided to the sub-transport path P2 and is transported along the sub-transport path P2.

In S408, the CPU 201 (speed condition determination unit 231) determines whether the reversal sensor 113 is turned on. That is, the CPU 201 determines whether the leading edge of the sheet has arrived at the detection position of the reversal sensor 113 based on the detection result of the reversal sensor 113. When the reversal sensor 113 is turned ON, the CPU 201 proceeds to S409.

In S409, the CPU 201 (speed changing unit 232) returns (increases) the rotational speed of the motor 204 from the second rotational speed to the first rotational speed via the drive circuit 203. As a result, the sheet conveyance speed returns to the first conveyance speed. Note that when the reversal sensor 113 is turned off (when the rear end of the sheet passes the reversal sensor 113), the CPU 201 switches the solenoid 205 to OFF. As a result, the reversing mechanism 300 is activated, and the direction of rotation of the FD roller 111 is switched from reverse rotation to normal rotation. The sheet is again passed to the registration roller 104 and further conveyed to the transfer section.

In S410, the CPU 201 (image forming control unit 220) controls the image forming apparatus 100 to form a toner image on the second side of the sheet. In S<b>411 , the CPU 201 (conveyance control unit 230 ) controls the image forming apparatus 100 to discharge the sheet on which images are formed on both sides to the FD tray 112 . In S411, the solenoid 205 is kept OFF, so the FD roller 111 continues to rotate normally.

FIG. 5 is a timing chart explaining the reversal timing. Time t1 is the timing when the trailing edge passes the predetermined position in S403, and is the timing when the fixing discharge sensor 109 is switched from on to off. At time t1, the rotational speed of the motor 204 is changed from the first rotational speed (normal speed) to the second rotational speed (low speed). Note that the solenoid 205 is OFF at time t1. Registration 105 is also OFF. Reversal sensor 113 is also OFF.

Time t2 is the time when a predetermined time Tb has elapsed from time t1. Time t2 is the time when the condition regarding the predetermined time Tb is satisfied in S406. At time t2, the solenoid 205 is turned on, and the sheet conveyance direction is reversed. At time t2, the rotational speed of the motor 204 is the second rotational speed.

Time t3 is the time when the leading edge of the sheet is detected by the reversal sensor 113 in S408. At time t3, the rotational speed of the motor 204 is changed from the second rotational speed to the first rotational speed.

In the first embodiment, the rotational speed of the motor 204 returns from the second rotational speed to the first rotational speed on the condition that the reversal sensor 113 is turned on. However, the CPU 201 may change the rotation speed of the motor 204 when a predetermined time Tc has elapsed from time t2, which is the timing at which the solenoid 205 was turned on. As shown in FIG. 5, the predetermined time Tc is the time from time t2 to time t3. The predetermined times Tb and Tc are determined in advance through experiments or simulations, are held in the ROM area of the storage device 210, and are read and used by the CPU 201.

In the first embodiment, the second rotation speed is defined as half of the first rotation speed, but this is only an example. The second rotation speed may be determined depending on the distance of the sheet reversing section including the FD roller 111 and the image forming speed. In other words, the second rotational speed may be any transport speed that allows the sheet to be reliably drawn from the main transport path P1 to the sub transport path P2 without being erroneously ejected onto the FD tray 112. In this way, by switching the rotational speed of the motor 204 to a low speed, the distance that the sheet is conveyed before being reversed is shortened. As a result, it is possible to downsize the reversing section of the image forming apparatus 100 while maintaining a good front-back reversing operation. In other words, even if a switchback method is adopted in which a part of the sheet is discharged outside the image forming apparatus 100 and the conveyance direction of the sheet is reversed, the front and back sides of the sheet can be successfully reversed. Moreover, since the sheet conveyance speed is increased once the reversal of the sheet is completed, the time required to form images on both sides of the sheet does not become so long. In other words, the productivity and usability of the image forming apparatus 100 are maintained.

<Example 2>
In the first embodiment, the motor 204 is decelerated using the turning off of the fixing discharge sensor 109 as a trigger. However, any trigger that can produce the same effects as in the first embodiment can be employed in the present invention. Therefore, in the second embodiment, the motor 204 is decelerated using the lapse of a predetermined time Td after the registration sensor 105 is turned off as a trigger. Items in Example 2 that are common to Example 1 are given the same reference numerals, and their explanations will be omitted.

FIG. 6 is a flowchart showing image forming processing according to the second embodiment. As described above, the motor 204 is activated in S401, and image formation on the first surface is started in S402. After that, the CPU 201 advances to S601.

In S601, the CPU 201 (speed condition determining unit 231) determines whether the detection signal of the registration sensor 105 has turned OFF. That is, the CPU 201 determines whether the rear end of the sheet has passed the detection position of the registration sensor 105. When the trailing edge of the sheet passes through the detection position of the registration sensor 105, the CPU 201 advances to S602.

In S602, the CPU 201 (speed condition determination unit 231) starts the timer 211. In step S<b>603 , the CPU 201 (speed condition determination unit 231 ) determines whether a predetermined time Td has elapsed from the timing when the trailing edge of the sheet passed the detection position of the registration sensor 105 . The predetermined time Td is the time required for the trailing edge of the sheet to be conveyed from the detection position of the registration sensor 105 to the nip portion of the fixing device 130. In other words, S603 is a process for determining whether the trailing edge of the sheet has arrived at the nip portion of the fixing device 130. When the predetermined time Td has elapsed, the CPU 201 proceeds to S604. In S604, the CPU 201 (speed changing unit 232) reduces the rotational speed of the motor 204 from the first rotational speed to the second rotational speed.

In S605, the CPU 201 (direction condition determination unit 233) determines whether the fixing discharge sensor 109 is turned off. That is, the CPU 201 determines whether the trailing edge of the sheet has passed the detection position of the fixing discharge sensor 109. When the detection signal of the fixing discharge sensor 109 changes from ON to OFF, the CPU 201 advances to S605.

In S606, the CPU 201 (direction condition determining unit 233) starts the timer 211 to measure a predetermined time Tb. After that, the CPU 201 executes S406 to S411.

FIG. 7 is a timing chart explaining the reversal timing. In this example, time t0 is the time when the detection signal of registration sensor 105 switches from ON to OFF. Time t1 is the time when a predetermined time Td has elapsed from time t0. At time t1, the rotational speed of the motor 204 is changed from the first rotational speed to the second rotational speed.

Time t2 is the timing at which the detection signal of the fixing discharge sensor 109 switches from ON to OFF. At time t2, timer 211 is restarted to measure a predetermined time Tb. Time t3 is a timing at which a predetermined time Tb has elapsed from time t2. At time t3, solenoid 205 is turned on. Time t4 is the timing at which the detection signal of the reversal sensor 113 switches from OFF to ON. At time t4, the rotational speed of the motor 204 is changed from the second rotational speed to the first rotational speed.

The predetermined time Td may be calculated from the following formula.

Td = (Lrf) / Vp (seconds) (1)
Here, Lrf is the distance (mm) from the detection position of the registration sensor 105 to the center of the nip portion of the fixing device 130. Vp is a first conveyance speed (mm/sec) corresponding to the first rotation speed.

As described in the second embodiment, the rotational speed of the motor 204 may be changed using the lapse of a predetermined time Td from the timing when the registration sensor 105 is turned off as a trigger. As a result, in the second embodiment, compared to the first embodiment, the distance over which the sheet is conveyed before the sheet is reversed will be shortened. Other effects and modifications of the second embodiment are as described in the first embodiment.

<Technical ideas derived from examples>
[Viewpoint 1]
The main conveyance path P1 is an example of a conveyance path that conveys sheets. The photosensitive drum 122 and the transfer roller 106 are an example of image forming means that forms images on the first and second surfaces of the sheet conveyed through the main conveyance path P1. The FD roller 111 is provided at the end of the main conveyance path P1, and functions as a switchback means that causes the roller to switchback the sheet on which an image is formed on the first surface. The sub-conveyance path P2 functions as a sub-conveyance path that conveys the switched-back sheet to the main conveyance path in order to form an image on the second surface of the sheet. Note that a flapper may be employed between the main conveyance path P1 and the sub-conveyance path P2 to guide the sheet conveyed by the reversely rotated FD roller 111 to the sub-conveyance path P2. Note that if the entrance of the sub-transport path P2 is provided above the main transport path P1, the flapper may be omitted. This is because when the near rear end of the sheet is nipped by the FD roller 111, the front end of the sheet becomes heavier with respect to the FD roller 111, and the rear end of the sheet tends to face upward (see-saw phenomenon). The motor 204 is an example of a motor that drives a roller provided in the switchback means and is controlled to rotate only in a fixed direction. Like the motor 204, a motor that drives a plurality of rollers provided on the main conveyance path P1 is basically driven to rotate only in one direction. The reversing mechanism 300 is an example of a transmission means that transmits the driving force supplied from the motor 204 to the roller. The solenoid 205 functions as a switching device that acts on the transmission device to switch the direction of rotation of the roller caused by the driving force between normal rotation and reverse rotation. CPU 201 is an example of a control means. The period before time t2 shown in FIG. 5 or time t3 shown in FIG. 7 is an example of a first period in which the sheet on which an image is formed on the first side by the image forming means is conveyed in the first direction by the roller. be. The period from time t2 to time t3 shown in FIG. 5 or from time t3 to time t4 shown in FIG. 7 is an example of a second period in which the sheet is conveyed by the roller in a second direction different from the first direction. It is. At least during the first period, the CPU 201 controls the motor so that the sheet is transported from a first transport speed, which is the transport speed at which the sheet is transported through the image forming means, to a second transport speed that is lower than the first transport speed. The rotation speed of 204 is controlled. As a result, it is possible to realize the downsizing of the image forming apparatus 100 and to successfully invert the sheet.

[Viewpoints 2 and 3]
At the second conveyance speed, the rotation direction of the rollers is switched by the switching means and the transmission means when the sheet is being conveyed to a conveyance position where the rear end of the sheet can enter the sub-conveyance path P2 while the sheet is being held between the rollers. The transport speed may be determined so that the process is completed. In other words, the second conveyance speed may be a conveyance speed determined such that switching of the rotational direction of the roller by the switching means and the transmission means is completed by the time the rear end of the sheet passes through the roller. This makes it difficult for a sheet on which an image is to be formed on the second side to be erroneously ejected to the FD tray 112.

[Viewpoint 4]
After the sheet conveyance direction is changed from the first direction to the second direction, the CPU 201 returns the sheet conveyance speed from the second conveyance speed to the first conveyance speed. That is, after the sheet is successfully reversed, the sheet conveyance speed is increased. This will facilitate successful inversion of the sheet.

[Viewpoint 5]
The registration sensor 105 and the fixing/ejection sensor 109 are examples of sensors that are provided upstream of the rollers in the sheet conveyance direction and detect the sheet conveyed through the main conveyance path. The CPU 201 may reduce the sheet conveyance speed from the first conveyance speed to the second conveyance speed based on the timing at which the sensor detects the leading edge or the trailing edge of the sheet.

[Viewpoint 6]
As described in Embodiment 1, a sensor (eg, fixing/ejection sensor 109) may be provided between the image forming means and the roller. When the trailing edge of the sheet passes the sensor, the CPU 201 may control the motor 204 to change the sheet conveyance speed from the first conveyance speed to the second conveyance speed.

[Viewpoint 7]
The sensor (eg, the fixing discharge sensor 109) may be a sheet sensor for confirming that the sheet is not jammed in the image forming unit. This would allow one sensor to be used for multiple purposes and reduce the number of sensors.

[Viewpoint 8]
The image forming means may include a fixing means (eg, fixing device 130) that fixes the toner image on the sheet. In this case, the sensor may be a sheet sensor (for example, the fixing discharge sensor 109) for confirming that the sheet is not jammed in the fixing unit. This would allow one sensor to be used for multiple purposes and reduce the number of sensors.

[Viewpoint 9]
The sensor (eg, registration sensor 105) may be provided upstream of the image forming means in the sheet conveyance direction on the main conveyance path. The CPU 201 controls the motor 204 to change the sheet conveyance speed from the first conveyance speed to the second conveyance speed at a timing when a first predetermined time has elapsed from the timing when the trailing edge of the sheet passes the sensor. good.

[Viewpoint 10]
The sensor may be a sheet sensor (eg, registration sensor 105) provided to determine the timing to start forming an image in the image forming means. This would allow one sensor to be used for multiple purposes and reduce the number of sensors.

[Viewpoint 11]
The first predetermined time may be a time (eg, Td) obtained by dividing the distance from the detection position of the sensor to the center position of the nip portion of the fixing means of the image forming means by the first conveyance speed.

[Viewpoint 12]
The CPU 201 may switch the conveyance direction of the sheet from the first direction to the second direction by switching the rotation direction of the roller based on the timing at which the sensor (eg, the fixing device 130) detects the trailing edge of the sheet.

[Viewpoint 13]
The CPU 201 may switch the rotation direction of the rollers using the fact that a second predetermined time period (e.g. Tb) has elapsed from the timing when the sensor (e.g. fixing device 130) detects the trailing edge of the sheet as a trigger. As a result, the conveyance direction of the sheet is switched from the first direction to the second direction.

[Viewpoint 14]
The reversal sensor 113 is an example of a detection means provided on the sub-transport path P2 to confirm that the sheet has been successfully transported to the sub-transport path. When the detection unit detects the leading edge of the sheet, the CPU 201 may return the sheet conveyance speed from the second conveyance speed to the first conveyance speed. In other words, after the reversal sensor 113 confirms that the sheet has been successfully reversed, the conveyance speed will be returned to the original speed.

The invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the claims are appended hereto to disclose the scope of the invention.

P1: Main transport path, P2: Sub-transport path, 111: FD roller, 201: CPU, 204: Motor, 205: Solenoid, 300: Reversing mechanism

Claims (14)

A main conveyance path for conveying sheets;
an image forming means for forming an image on a first surface and a second surface of the sheet conveyed through the main conveyance path;
a switchback means provided at the end of the main conveyance path and for switching back the sheet with an image formed on the first surface using a roller;
a sub conveyance path for conveying the switched back sheet to the main conveyance path in order to form an image on the second side of the sheet;
a motor that drives the roller provided in the switchback means and is controlled to rotate only in a certain direction;
a transmission means for transmitting the driving force supplied from the motor to the roller;
switching means acting on the transmission means to switch the direction of rotation of the roller caused by the driving force between normal rotation and reverse rotation;
A first period in which a sheet on which an image is formed on a first surface by the image forming means is conveyed in a first direction by the roller, and a second period in which the sheet is conveyed in a second direction different from the first direction by the roller. At least in the first period of the second period, from a first conveyance speed that is the conveyance speed at which the sheet is conveyed through the image forming means, to a second conveyance speed that is lower than the first conveyance speed. an image forming apparatus comprising: a control means for controlling a rotational speed of the motor so that the image forming apparatus is conveyed at The second conveyance speed is determined by the switching means and the transmission means when the sheet is being conveyed to a conveyance position where the rear end of the sheet can enter the sub conveyance path while being held between the rollers. The image forming apparatus according to claim 1, wherein the conveying speed is determined such that switching of the rotational direction of the roller is completed. The second conveyance speed is a conveyance speed determined such that switching of the rotational direction of the roller by the switching means and the transmission means is completed by the time the rear end of the sheet passes through the roller. The image forming apparatus according to claim 1, characterized in that: The control means is characterized in that after the conveyance direction of the sheet is changed from the first direction to the second direction, the control means returns the conveyance speed of the sheet from the second conveyance speed to the first conveyance speed. The image forming apparatus according to any one of claims 1 to 3. further comprising a sensor that is provided upstream of the roller in the sheet conveyance direction and detects the sheet conveyed through the main conveyance path;
2. The control means reduces the conveyance speed of the sheet from the first conveyance speed to the second conveyance speed based on a timing when the sensor detects a leading edge or a trailing edge of the sheet. The image forming apparatus described in . The sensor is provided between the image forming means and the roller,
The control means controls the motor to change the conveyance speed of the sheet from the first conveyance speed to the second conveyance speed when the rear end of the sheet passes the sensor. The image forming apparatus according to item 5. 7. The image forming apparatus according to claim 6, wherein the sensor is a sheet sensor for confirming that the sheet is not jammed in the image forming means. The image forming means has a fixing means for fixing the toner image on the sheet,
8. The image forming apparatus according to claim 7, wherein the sensor is a sheet sensor for confirming that the sheet is not jammed in the fixing means. The sensor is provided upstream of the image forming means in the conveyance direction of the sheet in the main conveyance path,
The control means controls the motor to change the conveyance speed of the sheet from the first conveyance speed to the second conveyance speed at a timing when a first predetermined time has elapsed from the timing when the trailing edge of the sheet passed the sensor. The image forming apparatus according to claim 5, wherein the image forming apparatus changes the conveyance speed. 10. The image forming apparatus according to claim 9, wherein the sensor is a sheet sensor provided to determine the timing at which the image forming means starts forming an image. The first predetermined time is a time obtained by dividing the distance from the detection position of the sensor to the center position of the nip portion of the fixing means of the image forming means by the first conveyance speed. The image forming apparatus according to claim 9 or 10. The control means switches the conveying direction of the sheet from the first direction to the second direction by switching the rotation direction of the roller based on the timing when the sensor detects the rear end of the sheet. The image forming apparatus according to any one of claims 5 to 11. The control means changes the conveyance direction of the sheet from the first direction by switching the rotational direction of the roller, triggered by the passage of a second predetermined time from the timing when the sensor detects the trailing edge of the sheet. The image forming apparatus according to claim 12, wherein the image forming apparatus switches to the second direction. further comprising a detection means provided on the sub-conveyance path and provided for confirming that the sheet has been successfully conveyed to the sub-conveyance path;
14. The control means returns the conveyance speed of the sheet from the second conveyance speed to the first conveyance speed when the detection means detects the leading edge of the sheet. The image forming apparatus described in .

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